Proper Prop and the Governor

[PLKennedy]

"Snow Goose" has a 16/10 three bladed prop, and will not rev greater than 2000 rpm.  In neutral, the M35 will not rev more than 2500 rpm.  Westerbeke says it should rev to 3000 rpm.

     1.     What is the correct size and pitch for of a three bladed prop for a c34?  The dealer says 15/10;

     2.     How does one adjust the governor so as to allow a maximum of 3000 rpm?

Peter

[msenko]

Peter,

Before worrying about the correct prop size for your boat, I would first try to figure out why the engine is not coming up to speed:

The governor is adjusted at the factory and adjustment should not be attempted unless you know EXACTLY what you are doing. The adjustment is usually set "for life" and it is unusual to have to make the adjustment. Also, if Snow Goose is a new boat, the governor is usually sealed at the factory and breaking the seal usually voids the engine warranty. I don't know specifically about the Universal diesel and how they treat this subject.

Are you running the stock factory supplied alternator?

Air and fuel are the only determinants, so I would make sure the air filter is clean and then change the fuel filter(s) to make sure you are getting enough of both. Do you have a prefilter like a Racor installed?

Are both high and low pressure fuel pumps delivering the proper volume of fuel?

If the engine still can't get up to speed, I would call a competent diesel mechanic and ask them to adjust it. They should have a hand held tach (which will be much more accurate than your console tach) with which to do this with. You can then adjust your own tach to match the mechanic's hand held. I usually set the engine at 2000 rpm's by the mechanic's tach and set the console tach accordingly. Incidentally, this needs to be done when you change the alternator shieve size.

As far as the prop size goes, as a general rule, you want to size the prop according to the largest that will fit on the boat. It is size that gives you efficiency, not pitch. When measuring the strut for prop size, the rule of thumb is to allow about 20% prop diameter clearance (3.2" for a 16" prop) from the tip of the prop to any under water structures. On the Cat34MK1's the 15" props are cutting into this margine at the hull. From there, you start adding pitch to get the proper engine rpm's. Since I am new to the list, I do not know if Snow Goose is a MK1 or MK2 version. I do not know what the clearances are on the MK2.

If you already have a 16" prop and it isn't showing signs of cavitation, then what about re-pitching the prop to 9?

Hope this helps,

Mike Senk

[Ron Hill]

Peter : First of all you've got the WRONG prop!! Look in the C34 Mainsheet Tech. Notes that I wrote back in Nov 99 on prop size. The factory should have installed a 3 bladed, SAILOR type (VERY Important), 15"x9" prop. Most of us have increased the pitch. DO NOT change the diameter.

Screw with the goveror seals and you can kiss your engine warrentee goodby. Playing with that item is the LAST resort!!

Low rpm has many causes (clogged filter, nasties growing on the prop, etc.), one of which is too large a prop.

In the next Mainsheet (Aug 01)I have another PROP article in the tech notes.

If looking at your C34 Tech note CD doesn't help let me know.   Ron

Ron, Apache #788

[PLKennedy]

"Snow Goose" is brandy new.  It is # 1590.  The engine has 27 hours on it, bringing it to Wickford RI from Marblehead MA, and doing a little cruising around Nassagansett Bay since we took delivery three weeks ago.  Everything is new.

Tomorrow we try the tach with a hand held to make certain that the tach is true.  After that, we'll check the prop size.  Dealer now thinks a 15/10 is better than the 16/10.

Thanks for the help, and keep the suggestions coming.

Peter

[jwwarwick]

Guys,
I have a 1989 C34 with the M25XP engine which I purchased in 1999. I was having the same problem of low RPM with clean prop and bottom. Since I did not know the history of service to the engine, I decided to first adjust the valve clearances on the engine before going any further. I picked up about 400 to 500 RPMs and the engine seemed to have a lot more power. It has been going strong ever since. You may want to try this if your engine valve clearances have not been regularly reset. John Warwick

[sail4dale]

My M35B engine on my 2001 Mk II wouldn't get up to speed (I thought).  Then I checked it with a hand tach.  AHA   it had an error that to correct needed a 1.25 factor.  I now just multiply the tach speed by 1.25 and that is my engine speed.  No I didn't change the adjustments on the tach.  I didn't feel it was worth the bother.  As long as I know what the speed is I don't worry.  My prop by the way is a Flexifold 15 x 10 pitch.  I can not get my engine revs up to 3000 in gear but I can motor at about 2400 RPM at 7-7.5 knots without smoke.  Fuel consumption at cruising is about .8 gal/hr

[Ron Hill]

Guys : It's dangerous to take the the RPM reading from the engine tach unless you have checked actual RPM and KNOW that your instrument readings are correct!!